Hi Deb,

Thank you for contacting University of Minnesota Extension about pruning your potentilla.

Potentilla are summer flowering shrubs that bloom on new growth produced earlier in spring. Another way of saying this is that they bloom on new wood. Consequently, these shrubs should be pruned in late winter or early spring, meaning from mid-February to early April. The answer to your question is to prune your potentilla soon.

If you were to wait until the last frost date in your area you would be pushing your pruning out into May. This would unnecessarily shorten the time the shrubs have to develop new wood and flower buds. Potentilla is hardy for your area so you normally don’t have to worry about frost killing the new growth.

The best method to encourage flowering on the potentilla is annual thinning and/or renewal. Thinning is done by cutting off a branch where it is attached to the main stem. Renewal, by removing older, woodier stems by cutting them off at the base of the shrub. This will encourage new stems to grow. When renewing, don’t remove more than 1/4 to 1/3 of the oldest canes each year. You’re not likely to have many old stems on your new shrubs, but as your potentilla ages you will need to start doing this each year. Never use hedge shears to prune the potentilla.

There is a nice picture and description of thinning on this Nebraska Extension page: https://lancaster.unl.edu/hort/factsheets/329prshr.shtml

When your potentillas start aging you will do more renewal pruning (removing stems from the ground up). This site shows a nice picture of how this looks from year to year. Scroll down to Figure 7. https://www.ag.ndsu.edu/publications/lawns-gardens-trees/basic-guidelines-for-pruning-trees-and-shrubs

For more general guidance on pruning trees and shrubs, this U of MN page also has some good information.

https://extension.umn.edu/planting-and-growing-guides/pruning-trees-and-shrubs

Hope this helps. Let us know if you have any other questions.

Ed C

Ramsey County Master Gardener